Pallet clamping systems have the advantage that the often lengthy clamping of a workpiece to be worked on a pallet can take place at a secondary place, while the machine tool works a different workpiece. After this working is finished it is possible to quickly remove the worked workpiece from the machine tool in a short time by pulling the pallet off from the machine tool table and it is possible also within a short time to move the workpiece to be worked into position for working by mounting the earlier equipped pallet on the machine tool table. The idle times of the machine tool are thus reduced to a minimum. Turntables which can receive two pallets are advantageously used for changing the pallets.
Known is a pallet clamping system, in which clamping bars are inserted in slots of machine tool tables, in which clamping bars are provided clamping cylinders. For this special slots are needed in the machine tool table, which slots have a substantially larger inside cross section than normal slots. Therefore during re-equipping of a machine tool for pallet clamping many modifications must be carried out on the machine tool table. Systems are also known for smaller pallets, in which conical pins are provided on the machine tool table, which pins engage holes in the pallet and onto which the pallet must be fixedly pressed by means of clamping mechanisms. Considerable modifications must in this system also be carried out on the machine tool table. Furthermore, it is known to laterally grip around the machine tool table with clamping elements. This also requires special tables. Furthermore the pallet can only be clamped at its outermost edge.
The basic purpose of the invention is to produce a pallet clamping system, in which without modification normal machine tool tables can have pallets clamped thereto.
This purpose is attained according to the invention, by the clamping mechanisms having cylinders, which are located completely within the pallet member, with at least one-sidedly hydraulically loadable pistons having secured thereon piston rods which project beyond the bearing surface and carry tongues, which fit in normal (i.e. conventional) table slots, for example T-slots, of a machine tool table.
When putting on a pallet the tongues are positioned so that they can be moved along the slots, when the pallet is moved above, or closely above, the machine tool table. When the pallet has reached its correct position relative to the working (i.e. machining) tools, the pallet is fixed by activating the cylinders, whereby the tongues are pulled fixedly against the upper walls of the slots.
In principle both double-acting hydraulic cylinders and also single-acting hydraulic cylinders can be used. It is particularly advantageous to produce the clamping force by springs and to utilize the hydraulic fluid only for releasing. This has the advantage that also after a long-lasting uncoupling of one pressure source for hydraulic fluid the clamping force is maintained. However, it is also possible to produce the clamping force hydraulically. In the case of the high sealing capability of hydraulic systems which can be achieved today, the clamping force is maintainable for a long time, even after uncoupling of the hydraulic liquid pressure source. A storage means which can balance out small pressure-medium losses is here formed by the hydraulic fluid itself, which with pressures as high for example as 500 bar, as may be used here, is compressed approximately 3 percent in volume. When hydraulic clamping is used, it is possible to produce the clamping release movement selectively also hydraulically or through spring force. When hydraulic clamping is used, of course a constant connection to the pressure source can also be maintained, so that even with a certain amount of leakage a loss of the clamping force is not created.
The cylinders can be arranged in different ways. An advantageous arrangement locates the cylinders at the corners of a rectangle, with the cylinders aligned in groups along the table slots. The arrangement should be such that the tongues of all cylinders are introduced into the table slots during a movement of the pallet parallel to the longitudinal direction of the table slots.
All clamping cylinders are connected advantageously to one single hydraulic coupling part. One avoids in this manner several hydraulic connections, which, however, in principle are also possible. The need for a hydraulic installation on the tool machine is avoided if the hydraulic fluid is supplied through a push rod which moves the pallet during changing of pallets. Guiding of the hydraulic fluid along the push rod can occur for example directly in said rod, which is for example easily possible in the case of a hydraulic cylinder or, however, through a parallel installed line, like a hose.
A mechanism for the mechanical coupling between push rod and pallet is provided. A sure supply and discharge of hydraulic fluid is achieved, if the mechanical coupling engages when the hydraulic coupling is completed. Hydraulic operation of the mechanical coupling has the advantage, that an additional control line or an additional manual operation is avoided. If, as is preferably the case, the hydraulic fluid is to be supplied and discharged through one line, it is advantageous.
Provision of a tunnel for the engagement of the push rod has the advantage that, during moving of a pallet onto the machine tool table, the push rod applies its force to the front part of the pallet, so that the moving force on the pallet is substantially pulling and not pushing. This is advantageous in order to avoid relative canting of the pallet and table and thus to avoid wear.
Additional means can be provided for exact positioning of the pallet on the table.